2007 Shelby GT500 - Boosted Beginnings Part 1

Running the total ignition timing up to 23 degrees but keeping the air/fuel curve down near a safe 11.0:1, the power output of the 5.4L jumped from 443 hp to 478 hp (pay no attention to the 484 hp listed on the dyno sheet-it was a spike at the end of the run). The additional timing improved power everywhere, from 1,500 to 6,200 rpm. It also had a positive effect on the torque curve, as the motor exceeded 400 lb-ft from 2,300 to 6,200 rpm and never dipped below 350 lb-ft. It looked like the new GT500 motor was going to follow in the footsteps of the '03-'04 Cobra motors, as one simple modification had improved the power output by a solid 35 hp.

The next modification was the one we were most excited about-more boost. Not surprisingly, Ford saw fit to equip the GT500 motor with a press-fit blower pulley. Removal is difficult, especially if eventual reuse of the stock pulley is in mind. It was difficult to remove without damaging it. Luckily for us, Metco supplied a series of pulleys designed to work with an adapter hub. The hub system allowed us to easily interchange pulley sizes after the installation of the press-fit hub. The pulley selection ranged from a stock replacement (roughly 3.00 inches) to a slightly smaller 2.77-inch version, down to the surprisingly thin 2.59-inch pulley. In stock trim, the Eaton supercharger mustered a peak boost pressure of 8.5 psi. Stepping down to the 2.77-inch Metco pulley resulted in a jump in boost of roughly 1 psi (to 9.5 psi). Stepping down even further to the 2.59-inch pulley brought the peak boost to 11 psi and the peak power numbers to an impressive 517 hp and 521 lb-ft of torque. Torque production from the supercharged Shelby exceeded 500 lb-ft from 2,900 to 5,000 rpm, making for one sweet powerband. Even down at 2,000 rpm, the 5.4L pumped out 450 lb-ft of torque.

It looks like the GT500 motor is every bit as receptive to power mods as the original '03-'04 Cobra motors, but here are a few things to ponder about the 5.4L motor in the new wonder Stang. While the Metco pulleys offered boost and power gains, there is a limit to the size of the blower pulley given the physical size of the Eaton blower snout. It is unlikely blower pulleys will go much smaller than the Metco 2.59-inch. When you combine this with the fact that a larger crank pulley may not be a reality on this motor (interference from front cover bosses much like the Ford GT motor), you have a situation that ultimately limits how much boost you can run on your mod motor.

Also note that the horsepower output exceeded the torque output on the stock run and the run made with the additional ignition timing. This situation changed once we installed the Metco blower pulleys, especially the smallest version. The torque production exceeding the horsepower production is a sign that the improvements offered by the additional boost were more pronounced at engine speeds below the power peak. This means the supercharger is nearing its flow limit. Of course, there is more power to be had with cams and a better inlet and exhaust system, but the smart money for big boost is not with the Eaton Roots-style blower. Rather, it's found in the upcoming Kenne Bell twin screw. See ya next month.

Kenne Bell Custom Tuning
As expected, changes to the factory timing and air/fuel curve produced positive effects. The additional 6 degrees of timing combined with a steady air/fuel curve of 11.0:1 improved the power output of the GT500 motor from 443 to 478 hp. Torque production jumped from 428 to 456 lb-ft, with more sizable gains realized at the lower rev ranges. There appeared to be more power with additional engine speed, but it should be noted that the long stroke of the 5.4L will produce excess piston speed. After the custom tuning, torque production from the supercharged 5.4L exceeded 400 lb-ft from 2,300 to 6,200 rpm.

Metco 2.59-inch Blower Pulley
Having a factory supercharged motor is a blessing indeed. Just check out the power gains offered by a somewhat simple pulley swap. The Metco pulley system included an adapter hub that made pulley changes a snap, though removing the stock pulley was a bit of a chore. The smallest 2.59-inch Metco pulley raised the peak boost pressure to 11 psi and the power output to an impressive 517 hp. Torque production exceeded 500 lb-ft from 2,900 to 5,000 rpm, peaking at 521 lb-ft. Gaining additional boost pressure from the Eaton Roots-style blower may be difficult, but the cure for the more-boost blues will come from Kenne Bell in the form of a twin-screw blower upgrade. Look for full testing next month (or as soon as KB has it ready).